I can see my house from here!

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How tall would a stack of 540,000,000 one-dollar bills be?

Tonight's Mega Millions lottery drawing is worth $540,000,000. If you won, and collected the money in one-dollar bills, and stacked them, how tall would the stack be?

A million one-dollar bills would be about 358 feet tall. So 540,000,000 one dollar bills would be 540x358 feet high, or 193,320 feet high. That's about 36 miles high.

Why do Venus and Jupiter appear so close when they're so far apart?

Recently after sunset Jupiter and Venus have appeared close in the western sky. If they're so far apart, how is this possible?

Venus is only visible a few hours before sunrise or after sunset. This is because its orbit is inside the orbit of the earth - closer to the sun than we are.

Jupiter, because its orbit is outside the orbit of earth, can appear anywhere in the night sky (actually, it can be in the day sky, too, but it isn't bright enough to see).

The reason Jupiter can appear "near" Venus is because we are looking across the solar system at it. Jupiter is somewhere on the OTHER side of the solar system from us.

What's the deal with "leap year," anyway?

Tomorrow's "leap day." This means we get an extra day this year: February 29th. Why?

It turns out that a year isn't exactly 365 days long. A year is more precisely 365 days and about six hours (or, about a quarter of a day). Every four years, the "solar year" is out of sync with the calendar year, so an extra day is added to the calendar year to catch up and resync the calendars.

It's not QUITE as simple as that, of course. Because it's not EXACTLY 365 days and six hours, over the course of a hundred years or so, things can get out of sync again. So years that end in "00"and are divisible by 400 (like the year 2000) are also leap years, but other years that end in "00" and aren't divisible by 400 (1900, for example) are not leap years.

Enjoy your extra day!

Can they hear us out there?

Mankind has been having a one way conversation with the universe since radio waves first began leaving our planet in the late 1800's. Every radio station, every TV station, every transmitter is beaming a signal off the planet. So who's listening?

Most likely, nobody.

Even though the radio waves travel at the speed of light, that's still a small area of our Milky Way galaxy. For the waves to reach all corners of the galaxy will take another 118,000 years!

More here!

The Moon and Jupiter at sunset, 2/26/12

What color is The Earth?

When you look up in the sky at night, you can often see the planet Mars. Mars looks like an orange-ish star in the nighttime sky. It got me to thinking, if you were on Mars, looking at the Earth, what color would Earth appear to be?

First, because Earth's orbit is inside the orbit of Mars, you would see "phases,' like we see of Venus, Mercury and The Moon. The only time you would see a "Full Earth" would be when the Moon and Earth are at opposite points in their orbits (across the Solar System from each other). And then, most of the time, the Sun would be in the way of seeing Earth from Mars. There's a cool animation of that concept here. 

In 2004, the Mars rover Spirit turned its cameras toward earth and took this picture:

This is the first image of Earth taken from the surface of another planet. Unfortunately, it's in black and white.

In orbit around Mars, the HiRISE camera on NASA's Mars Reconnaissance Orbiter took this picture of Earth and The Moon in 2007.

Here's another set of images - images of the Earth as seen from various space missions over the decades.